Arctic Amplification and Extreme Weather

A paper by Francis and Vavrus (2012) links the Arctic Amplification- AA (the observed enhanced warming of high northern latitudes relative to northern hemisphere) to some of the recent extreme weather in the mid-latitudes of Europe and North America. Specifically, the authors identify two effects of the AA to extreme weather, namely (1) a weakened zonal index and (2) increased wave amplitude, both contributing to slower eastward progression of the Rossby waves in the upper-level flow. The slower progression of upper-level flows causes associated weather patterns to become more persistent, which can lead to increased probability of extreme weather events such as droughts, flooding, cold spells and heat waves. The authors conclude by suggesting that some of the recent extreme weather events like the snowy winters of 2009/10 and 2010/11 in the eastern US and Europe, the historic drought and heat wave in Texas (southwestern US) and the record-breaking rains in US northeast during summer 2011 could be linked to the persistent weather pattern and in turn to the Arctic Amplification

The paper seems to provide an evidential support of 'increasing' extreme weather events and its linkage to the AA-Arctic Amplification and, by extension, to the human-added CO2-induced warming of the Arctic region. However, it is important to note that several recent papers (e.g., Benestad, 2010; Lockwood et al., 2010) have linked low solar activity to cold winters in Europe. There are also other landmark papers by Namias (1955; 1982) on persistent droughts in the US mid-west and their possible linkage to colder SST ( Sea Surface Temperature) in the northeast pacific which could produce persistent blocking patterns leading to protracted heat waves and associated droughts in the US mid-west (e.g., 1980 heat wave, 1952-54 droughts). Thus, it may still be quite some time before the many factors influencing extreme weather events, including an anthropogenic influence (if any), are understood and properly accounted for.